Linker symbol access from within Rust code clarification

[itsLydt]

Hello, I am writing a preemptive scheduler using this crate and have set up memory.x accordingly. For the scheduler to work I need to know some of the memory layout details, e.g. _stack_start and possibly some other info such as the heap start location. Per google's advice I have also written some code to access these symbols e.g.

    extern "C" {
        static _stack_start: u32;
    }

    pub fn stack_start() -> usize {
        unsafe { &_stack_start as *const u32 as usize }
    }

However, when reading the developer note in memory.x it states that symbols that start with a single underscore should not be accessed in this manner. I was wondering what is the intended way to access this information if not by the underscored symbols?

[jonathanpallant]

For the heap start, see https://docs.rs/cortex-m-rt/latest/cortex_m_rt/fn.heap_start.html.

For _stack_end, you can either ignore the advice and just refer to them anyway (but note they may change between cortex-m-rt revisions, so you should pin your version of cortex-m-rt); or you can just copy-and-paste our linker script into your project and make changes to export any symbols you require.

[itsLydt]

Ah thanks for the link! By "change between versions", does that mean change symbol names, same name but different value, or both?

[jonathanpallant]

We reserve the right to remove the symbols or change their names.